Exploring Novel Electronic Structures of Topological Quantum Matter

电子材料几乎在现代生活的各个方面都发挥着巨大的作用——从超级计算机到家用电器——这些材料中的电子行为决定了它们丰富而不寻常的特性。从历史上看，新型电子量子材料的发现给我们的生活方式和经济带来了革命，比如半导体的发现。最近，一种全新的电子材料，拓扑绝缘体，被理论预测和实验实现。拓扑绝缘体代表了一种全新的量子物质状态，它不同于所有已知的状态。从表面上看，它们是众所周知的、现成的材料；但它们具有深刻的、以前被忽视的特性，使它们如此独特。在其纯形式下，拓扑绝缘体在体电子带中具有完整的能隙（因此像绝缘体）；而在表面上，它是由具有线性能量-动量关系的电子（类似于不具有静止质量的光子！）形成的金属态，它们的自旋极化完全由它们的运动方向决定。更引人注目的是，这些不寻常的电子非常强大，可以在拓扑绝缘体表面流动，抵抗任何非磁性杂质、晶体缺陷或表面扭曲。由于具有重大的科学意义和技术潜力，拓扑绝缘体近年来已成为凝聚态物理研究的热点之一。然而，虽然世界各地的科学家都在推进这一令人兴奋的领域的前沿，但在我们真正实现许多惊人的量子现象（如磁单极子，半电子电荷和拓扑绝缘体中修正麦克斯韦方程产生的许多拓扑磁电效应）和实际应用（如新型电子，自旋电子和热电应用）拓扑绝缘体承诺之前，仍然存在许多挑战。例如，当前的拓扑绝缘体通常具有过多的散装载流子，从而阻止了散装绝缘（这将掩盖来自表面电子的微妙拓扑效应）；而体积能隙小也阻碍了它们在高温（室温）电子器件中的应用。因此，我们希望通过开展本项目来解决这些问题，提高现有拓扑绝缘子的质量，并寻找体积能隙更大、在常规环境下更稳定的更好的拓扑绝缘子。我们还将探索在实际应用中利用拓扑绝缘体不同寻常的电子和自旋特性的途径，如超低功耗电子，新型自旋电子器件，光电子应用，高效热电应用和催化应用。此外，拓扑绝缘体的迅速发展也激发了其他新的拓扑状态的研究，如量子反常霍尔绝缘体、拓扑半金属、拓扑晶体绝缘体和拓扑超导体等。这些新的拓扑态将为更丰富的奇异量子现象（如没有外部施加磁场的量子化霍尔电导，以及作为自身反粒子的奇异马约拉纳费米子）和更多非常规应用（从超低集成电路到未来的拓扑量子计算机）打开大门，因此我们也将在这个项目中寻找这些量子物质的新相位。

Electronic materials play a tremendous role in almost every aspect of modern life - from supercomputers to household electronics - and the behavior of electrons in these materials determines their rich and unusual properties. Historically, the discoveries of novel electronic quantum materials have caused revolutions in our lifestyle and economy, such as the discovery of semiconductors. Very recently, an entirely new type of electronic materials, the topological insulator, was theoretically predicted and experimentally realized.Topological insulators represent a brand new state of quantum matter that is distinct to ALL previously known states. On the face of it, they are well-known, off the shelf materials; but they have profound, yet previously overlooked properties that make them so unique. In its pure form, a topological insulator has a full energy gap in the bulk electron band (thus like an insulator); while on the surface, it has metallic states formed by electrons with linear energy-momentum relationship (similar to photons that do not possess rest mass!) with their spin polarization completely determined by their moving directions. More dramatically, these unusual electrons are extremely robust, and can flow on the surface of topological insulators against any non-magnetic impurities, crystalline defects or surface distortions. Due to the great scientific significance and technological potential, topological insulators have grown as one of the most intensely studied fields in condensed matter physics within the last few years.However, while the scientists worldwide are advancing the frontier of this exciting field, there remain many challenges before we can actually realize the many amazing quantum phenomena (such as the magnetic monopoles, half electron charge and many topological magneto-electric effects resulted from the revised Maxwell equations in topological insulators) and practical applications (such as novel electronic, spintronic and thermoelectric applications) topological insulators promise. For examples, current topological insulators typically have excessive bulk carriers, thus prevent the bulk from being insulating (which will mask the subtle topological effects from the surface electrons); and the small bulk energy gap also prevent them from being used in high (room) temperature electronic devices. Thus we would like to solve these problems by carrying out this project to improve the quality of current topological insulators, and search for even better topological insulators with larger bulk energy gap and more stable in regular environments. We will also explore the pathways to use the unusual electronic and spin properties of topological insulators in practical applications, such as ultra-low power electronics, novel spintronic devices, optoelectronic applications, high efficiency thermoelectric applications and catalysis applications.Furthermore, the swift development of topological insulators has also inspired the study of other new topological states, such as quantum anomalous Hall insulators, topological semi-metals, topological crystalline insulators and topological superconductors, etc. These new topological states will unlock the door to even richer exotic quantum phenomena (such as quantized Hall conductance without externally applied magnetic field, and the exotic Majorana fermions that are their own anti-particles) and more unconventional applications (from ultra-low integrate circuit to future topological quantum computers) Thus we will also search for these novel phases of quantum matter in this project.